Identification of the molecular and cellular mechanisms that cause vascular disorders defines the pathways that structure the vasculature during development and remodel the vasculature following injury in the adult. Our laboratory focuses on the role of cell cycle proteins, specifically the cyclin-dependent kinase inhibitors (CKIs), in regulating vascular development and vascular repair. We have pursued several lines of investigation. We previously had observed that inhibition of vascular smooth muscle cell proliferation in injured vascular tissues is regulated by the CKI p27. To determine how modifications in p27 alter proliferation responses, we cloned and characterized a kinase, kinase interacting strathum or KIS, that phosphorylates p27 at serine 10, leading to nuclear export of p27, phosphorylation on threonine 187 and proteolytic degradation by ubiquitination. KIS is activated by mitogens during G0/G1 phase of the cell cycle, and expression of KIS overcomes growth arrest induced by p27, leading to cell cycle progression. KIS may be an important differentiation factor in other cell systems, and therefore, we have investigated the structure and function of this protein further. We subsequently have sequenced and characterized the KIS promoter, confirming mitogen activation of the kinase. KIS is expressed in the developing heart, vasculature and brain where it functions to regulate cell proliferation and differentiation. In the developing heart, KIS appears to be regulated by transcription factors, critical for cardiac development. Other studies have pursued the expression and function of p27 in arterial wound repair and remodeling. In these studies, we have moved to analyses of genetically engineered mice. Mice lacking p27 have accelerated lesion formation following vascular stresses, due to uncheck proliferation of vascular smooth muscle cells, T-cell inflammatory responses, and altered collagen formation. Crosses with other CKI knock-out mice, including p21, and rag null mice are examining the mechanisms of inflammation and proliferation. Interestingly, a deficiency of p27 in an apoE null background severely accelerates atherosclerosis. Two other cell cycle proteins have been studied: protein arginine methyltransferase 2 (PRMT2) which regulates phosphorylation of the retinoblastoma gene product, Rb, and minichromosome maintaining protein 7 (MCM7), critical for initiation of DNA replication. To understand the relevance of cell cycle signaling pathways in human vascular disease, a clinical study of patients with coronary artery disease who are undergoing stent placement has been initiated. Patients who experience clinical restenosis will be compared to those patients whose percutaneous procedures are successful. Gene expression profiling and proteomic approaches are being used to investigate differences between patient groups. On the basis of gene and protein expression patterns, genotyping of patients is being conducted. These studies will use molecular profiling to predict outcome after percutaneous coronary interventions for coronary artery disease. Taken together, these studies define molecular and cellular signaling pathways important in the pathogenesis of vascular diseases. Understanding these pathways is critical to the design and development of new therapies for cardiovascular diseases.